\begin{tikzpicture}[>=Stealth]
    \foreach \pos/\text in {0/-3, 0.5/-1, 1/\hphantom{+}0, 1.5/+1, 2/+3, 2.5/+5} {
        \draw (0, \pos) node {$\text$} (0.3, \pos)[->] --(1, \pos);
        \draw (1.1, \pos) -- (1.5, \pos);
        \draw [->] (1.6, \pos) -- (3, \pos);
    }
    \node at (1.5, 3) {$+(-3)$};
    \node at (3.3, 2.5) {$+2$};

    \draw (1.5, 1.5) ellipse
        [x radius=1.1,y radius=2];

    \draw[decorate,decoration={brace,mirror,amplitude=0.2cm}] (-0.3, 2.5) -- (-0.3, 0)
        node [pos=0.5, left=1em, align=center] {输\\入};
    \draw[decorate,decoration={brace,mirror,amplitude=0.2cm}] (3.8, 0) -- (3.8, 2.5)
        node [pos=0.5, right=1em, align=center] {输\\出};
\end{tikzpicture}
